Cover body for air bag apparatus

ABSTRACT

A cover body of a vehicle air bag apparatus, including a covering portion which is formed integrally with an interior panel body and which has a door portion defined by a tear seam formed in a back of the interior panel body, and, a backing portion joined to a back of the covering portion. The covering portion is made of polyolefin resin having a flexual elastic modulus of from 1500 to 3500 MPa, a tensile strength of from 17 to 40 MPa, an Izod impact strength of from 3.0 to 15.0 kJ/m2, and an elongation of 400% or less. The backing portion is made of thermoplastic olefin which is softer and has a greater elongation. The backing portion includes a reinforcing portion at a back of the door portion, a surrounding base at the back of the covering portion, and a hinge portion joining the reinforcing portion and the surrounding base.

BACKGROUND OF THE INVENTION

This is a Continuation of U.S. application Ser. No. 11/481,006 filedJul. 6, 2006, which is a Divisional of application Ser. No. 10/667,376filed Sep. 23, 2003; the entire disclosures of the prior applications,are hereby incorporated by reference.

The present invention relates to a cover body for an air bag apparatuswhich is integrally formed with an internal panel of a vehicle. Thisinvention is applicable particularly, but not exclusively, to a coverbody for an air bag apparatus to be used for a front passenger seat, thecover body being formed integrally with an instrument panel.

Instrument panels located below the front window of a vehicle have beendesigned as instrument panels with hidden seamlines, which have anintegrated air bag apparatus comprising an air bag and an inflatorstored inside the instrument panel. Within the instrument panel, a lowerportion of the air bag apparatus is fixed to a steering member disposedalong the direction of the width of a vehicle, and an upper portionthereof is attached to a pair of attaching members consisting of a backand front member which are formed integrally with a rear of aninstrument panel.

Japanese Patent Provisional Publication 2001-39254 discloses an air bagapparatus wherein a door portion is formed in a portion of an instrumentpanel directly covering an air bag between a pair of attaching membersby the instrument panel itself being sectioned by a tear seam formed ina closed-loop shape on a back surface thereof.

By forming the door portion in the instrument panel itself in thismanner, an outer appearance of the instrument panel is maintained in anattractive state, as compared to forming an opening in the instrumentpanel and emplacing a separately formed lid which closes the opening andopens upon deployment of an air bag. An aluminum backing member isformed on a back inner side of the door portion, the backing memberextending past the tear seam to beyond the door portion. When the airbag inflates, the inflation force of the air bag pushes the entire doorportion by pushing through the backing member, and the door portion istorn along the tear seam and the door portion is torn away. The tornaway door portion swings outside to a front outer side of the instrumentpanel with a portion of the backing member directly under the tear seamacting as a hinge portion, and from the opening formed by the severeddoor portion, the air bag inflates into the interior of the vehicle.

However, according to the above related art, since the backing memberjoined to the back side of the door portion of the instrument panel ismetal (in the above example, aluminum), the inflation force of the airbag does not directly act on a portion of the tear seam which is coveredby the backing member. That is, as the backing member is formed frommetal and is therefore not soft, it is not possible for the inflationforce of the air bag to directly act on the portion of the tear seamcovered by the backing member. Rather, the tear seam is torn by forcebeing exerted through the entire metal backing member, which produces anindirect pushing effect against the entire door portion. Therefore, itis necessary for the air bag apparatus to use an inflator for inflatingthe air bag which is large-size and high-powered, in order for the tearseam to tear properly with certainty. Such a solution is a disadvantagewith respect to weight and cost.

To solve this problem, Japanese Patent Provisional Publication2002-347556 by the present applicant discloses an air bag apparatuswherein the backing member is made from a plastic material.Specifically, the backing member is made from a soft resin material, andthe location of the backing member directly under the tear seam receivesthe inflation force of an air bag, is pushed up, and easily deforms,thus allowing a pushing-up force to act directly against the tear seam.In more detail, a thermoplastic olefin elastomer resin is used asmaterial for the backing member, the resin having a flexual elasticmodulus of 6000 kgf/cm² or less, preferably 4500 kgf/cm² or less, and asan embodiment, 2800 kgf/cm².

Japanese Patent Provisional Publication (Heisei) 9-109816 discloses anarrangement where an instrument panel doubles as a passenger-side airbag cover, and a reinforcing portion is disposed on a back side thereof.Materials for the instrument panel and reinforcing portion in thiscombination are preferably a polyolefin and olefin elastomer,respectively. Specifically, the instrument panel is polypropylene resinwhich has an elongation of more than 300%, a flexual elastic modulus ofmore than 20000 kgf/cm², a temperature of deflection under load of morethan 120° C., and an Izod impact strength at 23° C. of more than 15kg•cm/cm. The reinforcing portion is made of an olefin elastomer whichhas a flexual elastic modulus of more than 3000 kgf/cm², and an Izodimpact strength at −40° C. of more than 20 kg•cm/cm.

Japanese Patent Provisional Publication (Heisei) 8-48204 discloses atwo-layer cover for a gas bag module where hardness of the first layeris in a range of approximately Shore D hardness 32 to 43, and hardnessof the second layer is in an approximate range of Shore A hardness 45 to80.

Also, in an instrument panel with hidden seamlines having an air bagapparatus integrally formed therewith as in the above examples, a bentgroove portion is formed in the backing member which is directly under alocation to constitute the hinge of the door portion.

A backing member made of thermoplastic polyurethane foam is disposed ona back side of a door portion, and extends beyond a tear seam and beyondthe door portion. Due to the inflation force during deployment of an airbag, the entire door portion is pushed up by force exerted through thebacking member, and the door portion is torn along the tear seam and iscompletely torn away. The torn away door portion swings outward to anoutside of the instrument panel with a portion of the backing memberdirectly under the tear seam acting as a hinge, and from an openingformed by the severed door portion, the air bag expands into theinterior of a vehicle.

SUMMARY OF THE INVENTION

However, such an air bag apparatus disposed inside an instrument panelmust be able to fulfill certain requirements for fully and properlyfunctioning as a safety device. For example, upon collision impact of avehicle, an inflator must be activated to instantaneously inflate an airbag, and a door portion of an instrument panel which forms an air bagcover must be torn along a tear seam by inflation force of the air bag,and the air bag must be inflated smoothly through an opening formed inthe instrument panel in the direction of a vehicle interior. Further,since this operation is to be performed within a vehicle whichexperiences a wide range of high and low temperatures, sufficientmechanical characteristics must be stably maintained throughout a widetemperature range in order for smooth operation of an air bag apparatusto be guaranteed under practical temperature conditions.

Further, an internally integrated air bag apparatus is desired to be inharmony with the entire instrument panel in which it is integrated,which also affects the appearance of the entire vehicle interior.

According to the related art, since a backing member joined to a backside of the door portion of the instrument panel joins an attachingportion (part of a supporting structure for an air bag apparatus) anddoor portion by a hinge portion which is U-shaped in cross-section,portions of a predetermined width not supported by the backing memberare formed at portions of the instrument panel which are directly overthe hinge portion. During inflation of the air bag, due to theseportions of the instrument panel not being supported, the instrumentpanel itself receives the impact of the air bag. Thus, it is necessaryfor the instrument panel to possess a high impact resistance which isnot otherwise normally required in an instrument panel. This is a factorwhich increases cost. And since the hinge portion of the backing memberis of a predetermined width, stress is concentrated at portions of thebacking member which are in contact with the door portion duringinflation of the air bag. This leads to a possibility of unintendedtearing, such as cracking occurring at portions other than the tearguide portion of the door portion. In such instances, an opening for theair bag to expand through, which also serves as an air bag pathway, isthus not properly formed along the intended tear guide portion.

It is therefore an object of the present invention to provide a coverbody for an air bag apparatus which is superior in safety andreliability, also durability and appearance, across a wide range oftemperatures.

It is another object of the present invention to provide a cover bodyfor an air bag apparatus which is capable of properly tearing a tearseam which is covered by a backing member, such that a desirableexpansion path will be formed, across a wide temperature range.

An aspect of the present invention resides in a cover body covering anair bag apparatus, the cover body being integral with an interior panelof a vehicle. The cover body comprises a covering portion formedintegrally with an interior panel body, the covering portion having adoor portion defined by a tear seam formed in a closed-loop shape in aback surface of the interior panel body, and, a backing portion which isjoined to a back of the covering portion including the door portion. Thecovering portion is made of polyolefin resin which has a flexual elasticmodulus of from 1500 to 3500 MPa, a tensile strength of from 17 to 40MPa, an Izod impact strength of from 3.0 to 15.0 kJ/m², and anelongation of 400% or less. The backing portion is made of thermoplasticolefin which is softer and has a greater elongation than the polyolefinresin. The backing portion comprises a reinforcing portion joined to aback surface of the door portion, a surrounding base which is joined tothe back surface of the covering portion surrounding the door portionand having an attachment portion, and a hinge portion having an endjoined to the reinforcing portion and another end joined to thesurrounding base.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an instrument panel and an airbag apparatus formed integrally therewith according to a firstembodiment of the present invention.

FIG. 2 is a perspective view of the instrument panel of FIG. 1 showing adoor portion and a backing member on a back side of the door portion.

FIG. 3 is a cross sectional view of the backing member of FIG. 1.

FIG. 4 is an enlarged cross-sectional view of a hinge portion of thedoor portion and the backing member of FIG. 1.

FIG. 5 is an underside view of the instrument panel of FIG. 1 showingthe layout of a tear seam.

FIG. 6 is a diagram of the door portion of FIG. 1 showing a process ofthe door portion opening.

FIG. 7 is a perspective view of the instrument panel and the air bagapparatus of FIG. 1 showing a joining rib portion on the backing member.

FIG. 8 is a plan view of the backing member showing the joining ribportion of FIG. 7.

FIG. 9 is a cross-sectional view of the instrument panel and backingmember showing the joining rib portion of FIG. 7.

FIG. 10 is a perspective view of the instrument panel and backing memberof FIG. 1 showing door reinforcing portions according to a secondembodiment of the present invention.

FIG. 11A is a cross-sectional view of the instrument panel and backingmember of FIG. 10 taken along the line XIA-XIA.

FIG. 11B is a cross-sectional view of the instrument panel and backingmember of FIG. 10 taken along the line XIB-XIB.

FIG. 12 is a cross-sectional view of the instrument panel and backingmember of FIG. 10 showing a second modification thereof.

FIG. 13 is a cross-sectional view of the instrument panel and backingmember of FIG. 10 showing a third modification thereof.

FIG. 14 is a cross-sectional view of the instrument panel and backingmember of FIG. 10 showing a fourth modification thereof.

FIG. 15 is a plan view of the instrument panel of FIG. 10 showing apattern of individual holes in a cover layer.

FIG. 16 is an enlarged cross-sectional view of the tear seam of theinstrument panel of FIG. 15.

FIG. 17 is an enlarged cross-sectional view of the tear seam of theinstrument panel of FIG. 15 showing a fifth modification thereof.

FIG. 18 is an enlarged cross-sectional view of the instrument panel andthe backing member showing a joining portion extending from an extendedsupporting portion according to a third embodiment of the presentinvention.

FIG. 19 is a cross-sectional view of the instrument panel and air bagapparatus taken along the line XIX-O-O-XIX of FIG. 21.

FIG. 20 is a perspective bottom view of the instrument panel and backingmember of FIG. 18.

FIG. 21 is a bottom view of the instrument panel and backing member ofFIG. 18.

FIG. 22 is an enlarged portional view of FIG. 21.

FIG. 23 is an enlarged cross-sectional view of the instrument panel andbacking member showing a hinge portion with a lowered joining portionaccording to a fourth embodiment of the present invention.

FIG. 24A is an enlarged cross-sectional view of the hinge portion ofFIG. 23 during initial inflation stage of an air bag.

FIG. 24B is an enlarged cross-sectional view of the hinge portion ofFIG. 23 following the initial inflation stage shown in FIG. 24A.

FIG. 25 is an enlarged cross-sectional view of the hinge portion of FIG.23 showing a modification thereof.

FIG. 26A is a cross-sectional view of a hinge portion according to therelated art showing development of a crack.

FIG. 26B is a cross-sectional view of the hinge portion of FIG. 26Aafter expansion of an airbag showing a damaged portion resulting fromthe crack.

FIG. 27A is a cross-sectional view of a hinge portion according to therelated art before expansion of an air bag.

FIG. 27B is a cross-sectional view of the hinge portion of FIG. 27Aafter expansion of the air bag.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 to 9, there is discussed a first embodiment of acover body for an air bag apparatus in accordance with the presentinvention.

A cover body for an air bag apparatus of the first embodiment comprisesa covering portion 11 formed integrally with an instrument panel 1 of avehicle which is disposed below a front window 2, and a backing member22 which is attached to an inner side of covering portion 11 as asupport member. Since covering portion 11 is formed integrally withinstrument panel 1, it will be understood that the ensuing discussion ofinstrument panel 1 also infers covering portion 11. Instrument panel 1is a molded element formed with hard polypropylene resin having aflexual elastic modulus of 30300 kgf/cm² (3092 MPa), a surface of whichis close-grained to a matte finish to prevent reflection from frontwindow 2. Further, best results are achieved by using hard syntheticresin having a flexual elastic modulus of 14700 kgf/cm² (1500 MPa) ormore (preferably 19000 kgf/cm² (1939 MPa) or more) for instrument panel1. Material used for covering portion 11 has a flexual elastic modulusof from 1500 to 3500 MPa, a tensile strength of from 17 to 40 MPa, anIzod impact strength from 3.0 to 15.0 kJ/m², and an elongation of 400%or less.

Air bag apparatus 3 is disposed inside of instrument panel 1, that is,on a side of instrument panel 1 that is invisible to occupants insidethe vehicle.

Air bag apparatus 3 comprises a reaction can 5, an inflator 4 containedinside reaction can 5, and a bracket 6 which fixes reaction can 5 to asteering member 7. A mid-retainer 5 a is fixed to reaction can 5. An airbag 9 is folded and stored inside a case 8, and reaction can 5 forms asingle integral unit with case 8. Arrays of hooks 10 are arranged atboth sides of case 8, respectively.

A rectangular door portion 26 is formed in covering portion 11, coveringportion 11 being directly over a top portion of airbag apparatus 3. Doorportion 26 is defined in covering portion 11 by a tear seam 24 formed ina back side or surface of instrument panel 1, i.e., in an inner sidethereof invisible to occupants of the vehicle, such that the back sideof instrument panel 1 is divided into two sections, and appears as twoadjacent rectangles, as shown in FIG. 5. Tear seam 24 is a cut outgroove formed by machining with a rotating blade (such as a millingblade) after instrument panel 1 has been formed. Preferably, a thicknessof tear seam 24 is from 0.1 to 1.5 mm, 0.3 mm in this embodiment, andthus, irregularities or similar malconformations are avoided which canfrequently occur on a surface of an instrument panel facia by formingsuch tear seams by molding process. However, tear seam 24 can besimultaneously formed by molding process of instrument panel 1. In sucha case, there would be a resultant lowering of production cost.

A backing member 22 is joined to a back surface of covering portion 11including door portion 26 of instrument panel 1. Injection-moldedbacking member 22 is made from soft thermoplastic olefin elastomer (TPO)resin having a flexual elastic modulus of 2800 kgf/cm² (268 MPa).Further, material other than TPO resin can be used for backing member22, with good results being obtained by using any variety of softelastomer resin, e.g., TPU, TPE, SES, SEBS, as they are commonly known.Good results are also achieved with material having a flexual elasticmodulus of 6000 kgf/cm² (612 MPa) or less (preferably, 4500 kgf/cm² (459MPa) or less). The thermoplastic olefin elastomer of backing portion 22is softer and has a greater elongation than the polyolefin resin ofcovering portion 11. Backing member 22 is larger in size than doorportion 26 and extends beyond tear seam 24 to outside tear seam 24, anda lattice-shaped joining rib portion (not shown) is disposed both insideand outside tear seam 24. The joining rib portion is melted so as to befusable through a process of ultrasonic vibration welding. Joining forcebetween backing member 22 and instrument panel 1 is thereby achieved,and there are no adverse effects on the close-grained matte finish onthe surface of instrument panel 1. Also, since many joining points areformed at free locations on backing member 22, the joining force betweenboth backing member 22 and instrument panel 1 is increased.

It is important that the material used for covering portion 11 possessthe aforementioned characteristics. Specifically, in an instance whereits elastic modulus is less than 1500 MPa, the load-bearing ability ofthe material is insufficient, and material deforms too easily and itbecomes difficult to maintain appearance of the instrument panel. On theother hand, if its elastic modulus exceeds 3500 MPa, door portion 26 istoo strong when operation of air bag apparatus 3 is effected uponcollision impact of a vehicle, and much greater power to inflate air bag9 for smooth tearing of tear seam 24 is necessary. Preferable flexualelastic modulus is within a range of from 2000 to 3200 MPa, and morepreferably, from 2500 to 3000 MPa. In an instance where tensile strengthis less than 17 MPa, shock impact of a collision which is insufficientto effect deployment of air bag 9 will nevertheless be sufficient tocause damage along tear seam 24 by instrument panel 1 and thereforecovering portion 11 receiving the force of the shock. Also, in aninstance where tensile strength is more than 40 MPa, it is not quiteeasy to rip tear seam 24 stably along the shape it is designed in ausual condition range. Preferable tensile strength is in a range of from20 to 35 MPa, more preferably, from 23 to 30 MPa.

In an instance where the Izod impact strength is less than 3.0 kJ/m² orbeyond 15 kJ/m², it is not easy to rip tear seam 24 stably along theshape it is designed in a usual condition range. Preferable Izod impactstrength is in a range of from 3.8 to 7.5 kJ/m², more preferably from4.0 to 6.0 kJ/m². Further, in an instance where the elongation exceeds400%, it is not easy to rip tear seam 24 stably along the shape it isdesigned in a usual condition range. A preferable elongation is in arange of from 30 to 400%, more preferably from 100 to 400%.

Resin material used for covering portion 11 and backing member 22according to the present invention are chosen from among commerciallyavailable products.

A tube body 16 which is substantially cylindrical and square is formedat a position both close to and beyond tear seam 24 of backing member22, and comprises an attachment portion 17, 18 which constitute frontand back facing surface portions respectively of tube body 16. Sincebacking member 22 is formed from resin, attachment portion 17, 18 iseasily formed integrally therewith. Each facing surface portion ofattachment portion 17, 18 respectively comprises an attachment hole 19,onto which the arrays of hooks 10 of air bag apparatus 3 attach.

A base portion of each facing portion of attachment portion 17, 18 isformed in a substantial L-shape in cross-section and extends outward toform an inner surrounding portion 35 as an outer peripheral flange whichis square and flat. The joining rib portion is also formed on a surfaceof inner surrounding portion 35 which faces with the back side ofinstrument panel 1, that is, which faces with the back surface ofcovering portion 11, joining force with instrument panel 1 being thusachieved.

The joining rib portion will be explained with reference to FIGS. 7 to9. While door portion 26 is shown as only a single opening door swingingfrom only one edge thereof in FIGS. 7 to 9, it will be understood thatdoor portion 26 is not limited in this manner, and that FIGS. 7 through9 are meant to aid understanding of the relative disposition of the ribportion. Thus, referring to FIGS. 7 and 8, a joining rib portion 46comprising a plurality of joining ribs is formed on a surface of backingmember 22 which faces instrument panel 1. Joining rib portion 46comprises first rib portion 51, second rib portion 52, and third ribportion 53, which are formed having a uniform projecting dimension orheight selected from 1 to 3 mm, 2 mm in this embodiment. Also, secondrib portion 52 and third rib portion 53 are formed with a breadth-wisedimension or width selected from 1 to 3 mm, 1 mm in this embodiment.

First rib portion 51 is formed to have an angle of ±30° with respect toa length-wise direction of backing member 22 which is the direction ofreciprocative movement of vibration welding of instrument panel 1 andbacking member 22, i.e. the width-wise direction of the vehicle. Thatis, first rib portion 51 is formed in the direction of the width of thevehicle.

Also, as shown in FIGS. 7 and 8, the pitch or space between adjacentribs of first rib portion 51 is formed to be from 3 to 10 mmrespectively on both inner surrounding portion 35 and door reinforcementportion 33. First rib portion 51 formed on inner surrounding portion 35comprises a front fixing rib portion 54 formed at a front of a frontedge portion of a separation portion 20, a rear fixing rib portion 55formed at a rear of a rear edge portion of separation portion 20, and alateral fixing rib portion 56 which is formed on a side of both sideedge portions of separation portion 20.

Front fixing rib portion 54 and rear fixing rib portion 55 are formedalong the entire lengths of the front edge portion and rear edge portionof separation portion 20. Also, front fixing rib portion 54 and rearfixing rib portion 55 are formed symmetrically to one another in thefore and aft direction of backing member 22. Further, a portion of frontfixing rib portion 54 and rear fixing rib portion 55 which is near tearseam 24 and therefore near separation portion 20, specifically, aportion which is 20 mm or less of tear seam 24, preferably 10 mm orless, is formed having a width in a range of from one to three times awidth of second rib portion 52 and third rib portion 53, and is formedwith preferably two times a width of second rib portion 52 and third ribportion 53, i.e., 2 mm, and a pitch of from 3 to 5 mm.

Lateral fixing rib portion 56 comprises a front lateral fixing ribportion 61 formed at a front of both side edge portions of separationportion 20, a rear lateral fixing rib portion 62 formed at a rear ofboth side edge portions of separation portion 20, and a middle fixingrib portion 63 formed between front lateral fixing rib portion 61 andrear lateral fixing rib portion 62. Front lateral fixing rib portion 61and rear lateral fixing rib portion 62 are respectively disposed at adistance from front fixing rib portion 54 and rear fixing rib portion55. A pitch between individual ribs of front lateral fixing rib portion61 and rear lateral fixing rib portion 62 is substantially equal to aportion of front fixing rib portion 54 and rear fixing rib portion 55which is closest to separation portion 20. A pitch of individual ribs ofmiddle fixing rib portion 63 is formed wider than that of front lateralfixing rib portion 61 and rear lateral fixing rib portion 62, and pitchis somewhat narrower near a center zone taken in a front and backdirection at both edges of separation portion 20.

First rib portion 51 formed on door reinforcement portion 33 comprises afront opening rib portion 64 formed at a rear of the front edge portionof separation portion 20, a back opening rib portion 65 formed at afront of the rear edge portion of separation portion 20, and a middleopening rib portion 66 formed between front opening rib portion 64 andback opening rib portion 65. Front opening rib portion 64 and backopening rib portion 65 are respectively formed between front lateralfixing rib portion 61 and between rear lateral fixing rib portion 62, asextensions of front lateral fixing rib portion 61 and rear lateralfixing rib portion 62. A pitch of individual ribs of front opening ribportion 64 and back opening rib portion 65 is substantially equal to thepitch of front lateral fixing rib portion 61 and rear lateral fixing ribportion 62.

Further, each rib of middle opening rib portion 66 is formed with asmaller width than front opening rib portion 64 and back opening ribportion 65. Also, middle opening rib portion 66 is formed having a widerpitch than front opening rib portion 64 and back opening rib portion 65,a pitch thereof being somewhat narrower in a center zone thereof in thefront and back direction of door reinforcement portion 33.

Second rib portion 52 is formed along the fore and aft direction to besubstantially perpendicular to first rib portion 51. Accordingly, secondrib portion 52 is formed having an angle of ±60° or more relative to thedirection of reciprocative movement of vibration welding. Also, secondrib portion 52 has a width smaller than first rib portion 51. Further,second rib portion 52 is formed both on an entire surface of doorreinforcement portion 33 as well as on inner surrounding portion 35 atboth side edge portions of separation portion 20. A pitch betweenindividual ribs at a portion of second rib portion 52 near tear seam 24and therefore near separation portion 20, specifically, a pitch at aportion of second rib portion 52 within at least 20 mm of tear seam 24,preferably within 10 mm, is from 3 to 10 mm, preferably 4 mm.

Also, a portion of second rib portion 52 in the center zone in awidth-wise direction of door reinforcing portion 36 is formed with awider pitch than a portion thereof located in proximity to separationportion 20.

Accordingly, a portion of joining rib portion 46 along and near tearseam 24 is formed in greater density than a portion thereof not inproximity to tear seam 24 owing to the particular dimensions of frontfixing rib portion 54, rear fixing rib portion 55, front lateral fixingrib portion 61, rear lateral fixing rib portion 62, and second ribportion 52.

Further, third rib portion 53 is formed along a direction parallel tosecond rib portion 52 which is formed in a predetermined direction, andindividual ribs thereof have a width substantially equal to the width ofribs of second rib portion 52. Third rib portion 53 is formed on innersurrounding portion 35, and a pitch between individual ribs thereof isselected from 5 to 30 mm, 5 mm in this embodiment.

As a result, joining rib portion 46 is formed in a lattice shape. Also,according to the first embodiment, a surface area of a welding area ofbacking member 22 is formed to be, for example, 660 cm², and joining ribportion 46 is welded to have a total surface area of 150 cm². Thiswelding area of backing member 22 is a joined portion of instrumentpanel 1 and backing member 22, that is, an upper surface of backingmember 22 which faces the back side of instrument panel 1. Therefore,joining rib portion 46 occupies 22.7% of the surface area of the uppersurface of backing portion 22. Accordingly, joining rib portion 46 has asurface area in a range of from 10 to 30% of the surface area of theupper surface of backing member 22 which faces the back side ofinstrument panel 1.

Instrument panel 1 and backing member 22 are placed in a vibrationwelding machine, and with instrument panel 1 in a fixed state, doorreinforcement portion 33 and inner surrounding portion 35 of backingmember 22 are positioned and aligned over door portion 26 and an outersurrounding portion 25 respectively. Outer surrounding portion 25 is aportion of covering portion 11 which is around or encircles door portion26. Backing member 22 is pressed to the back side of instrument panel 1,and backing member 22 is vibrated in the length-wise direction.

Through the vibration process, first rib portion 51 of joining ribportion 46 made of TPO resin melts to become melted resin between theflat joining surface of joining rib portion 46 and instrument panel 1which are in mutual contact. A join portion or weld layer is therebyformed between instrument panel 1 and backing member 22.

According to the first embodiment, by reinforcing in a direction whichintersects the reciprocative direction of vibration welding of joiningrib portion 46, weld strength is improved and an expected weld strengthis obtained, as compared to an instance where a width of first ribportion 51 is less than a width of second rib portion 52 and third ribportion 53. It is therefore easy to regulate the amount of strengthduring the welding process. Also, less welding energy is required, andan undue concentration of local welding energy is prevented, as comparedwith an instance where a width of first rib portion 51 is larger thanthree times a width of second rib 52 and third rib 53, as in, forexample, an instance where instrument panel 1 and backing member 22 arejoined by a substantially complete surface welding. Instrument panel 1and backing member 22 are therefore easily and securely welded.

Certain advantages can be realized by joining rib portion 46 having asurface area of from 10% to 30% of the surface area of the joinedportion between instrument panel 1 and backing member 22. Regulation ofstrength during the welding process is performed more easily and weldstrength is better than in an instance where joining rib portion 46 isless than 10% of the surface area of the portion where instrument panel1 and backing member 22 are joined. Also, energy necessary for vibrationwelding of instrument panel 1 and backing member 22 is less than in aninstance where joining rib portion 46 is more than 30% of the surfacearea of the portion where instrument panel 1 and backing member 22 arejoined. And since this energy is easily applied in an even manner,instrument panel 1 and backing member 22 are easily welded together.

Since the density of joining rib portion 46 is small at a portionthereof not in proximity to tear seam 24, instrument panel 1 and backingmember 22 are easily welded together.

Thus, weld strength is improved in a portion around and in proximity totear seam 24 and a predetermined weld strength is achieved, and tearseam 24 tears properly due to pressure of expansion of air bag 9. Doorportion 26 thereby forms properly and smoothly, and thus an opening forair bag 9 to pass through upon deploying is smoothly and properlyformed.

Also, an amount of welding heat during welding of instrument panel 1 andbacking member 22 is maintainable at a necessary minimum. Further,undesirable effects due to inappropriate welding heat are prevented,such as damage to the outer appearance of instrument panel 1, ordeformation of instrument panel 1.

Since backing member 22 is a separate and individual element frominstrument panel 1, an angle of each facing portion of attachmentportion 17, 18 is set freely without forming undercuts in molds forinstrument panel 1. Since attachment portion 17, 18 is formed as a pairof front and back facing surface portions, the strength thereof isincreased, support strength of air bag apparatus 3 is improved, and theability of tube body 16 to guide the direction of inflation of air bag 9is enhanced. Further, as attachment portion 17, 18 is formed integrallywith backing member 22, an increase in the number of components isavoided.

A separation portion 20 is formed as a small-width slit in an H-shapesuch that door portion 26 is adjoined at a front and rear edge portionthereof at a portion of backing member 22 directly covering tear seam24. A portion of backing member 22 directly under a portion of tear seam24 at the front edge portion and rear edge portion of door portion 26 isformed into a hinge portion 37 which is a bent shape and disposedastride tear seam 24. Separation portion 20 is therefore formed underand along tear seam 24. Further, while separation portion 20 is formedas a portion where there is complete separation or detachment accordingto the first embodiment, separation portion 20 is formed as a weakportion as a second modification of the first embodiment. That is,separation portion 20 is formed as a thin, tearable connecting portion.Otherwise, this modification of the first embodiment is the same as thefirst embodiment.

Backing member 22 is explained with reference to FIG. 3. Hinge portion37 comprises a door-side portion 37 a, a first inclined portion 37 b, areflexing portion 37 c, a second inclined portion 37 d, and anattachment-side portion 37 e. Hinge portion 37 is formed in a bent elbowshape, first inclined portion 37 b being adjacent to reinforcementportion 33, and second inclined portion 37 d being adjacent to innersurrounding portion 35. As explained, according to the first embodiment,hinge portion 37 comprises a front member under a front edge portion ofdoor portion 26 and a back member under a back edge portion of doorportion 26. Hinge portion 37 can exist along one edge of door portion 26in an instance where door portion 26 swings centered at only one edgethereof, or, along two different edges, as in a double-door arrangement,in an instance where door portion 26 comprises two portions whichrespectively swing from different edges.

Inflation behavior of air bag 9 will now be explained. Upon collision ofa vehicle, gas is injected into air bag 9 from inflator 4. Air bag 9expands inside of case 8, and due to the expansion force, doorreinforcement portion 33 of backing member 22 and door portion 26 arepushed upward. Tear seam 24 formed in the shape of two adjoinedrectangles then tears in advance of the front member and the back memberof hinge portion 37, and door portion 26 opens as a double-door centeredabout hinge portion 37. As a result, tearing of door portion 26 isproperly performed, and door portion 26 is torn away from instrumentpanel 1, that is, from covering portion 11.

Door portion 26, which has torn away from instrument panel 1, opens byswinging in a front direction and a back direction centered about hingeportion 37 of backing member 22, and an opening is formed in the portionfrom which door portion 26 has been severed. Air bag 9 then inflatesfrom this opening into the vehicle interior to protect a passenger.During inflation of air bag 9, since hinge portion 37 of backing member22 is a bent shape which includes first inclined portion 37 b and secondinclined portion 37 d which are both straight-shaped flat portions,pushing and forcing of attachment-side portion 37 e in the direction ofattachment portion 17,18 is prevented when door portion 26 is swingingoutward to the outside of instrument panel 1, and as a result, an angleof attachment-side portion 37 e relative to the surface of instrumentpanel 1 (angle θ shown in FIG. 4) is prevented from becoming an acuteangle where hinge portion 37 is compressed in the direction ofattachment portion 17, 18. Also, a circumferential length of hingeportion 37 is maintained, and bending deformation is not concentrated atpoints including door-side portion 37 a, attachment-side portion 37 e,and reflexing portion 37 c which naturally have a bending point. Thus,referring to FIG. 6, since bending occurs easily at straight-shapedfirst inclined portion 37 b and second inclined portion 37 d, edges ofdoor portion 26 do not contact with the surface of instrument panel 1whereby movement of door portion 26 is limited, that is, the surface ofinstrument panel 1 does not interfere with door portion 26 and the edgesof door portion 26 do not ride on instrument panel 1. Also, the edges ofdoor portion 26 are above hinge portion 37 and therefore are preventedfrom contacting with air bag 9 by a bottom surface of hinge portion 37.Therefore, an opening for deployment and expansion of air bag 9 issecured, and smooth inflation of air bag 9 is promoted. No force acts onhinge portion 37 to pull hinge portion 37 outside, and localized bendingand tensile force at attachment-side portion 37 e is suppressed.

According to the first embodiment, parts which are straight-shaped arefirst inclined portion 37 b and second inclined portion 37 d. Thus,without setting an inclination angle thereof at a right angle to thesurface of instrument panel 1 which is adjacent to a base thereof,attachment-side portion 37 e is previously formed with an obtuse angleso as to open outward toward tear seam 24. As shown in FIG. 4, theinclination angle is set to be larger than 100°. For best results, theinclination angle is set at from 120° to 150°, and preferably at from125° to 145°. In the same manner, besides forming door-side portion 37 ato be at a right angle as in the first embodiment, door-side portion 37a is set with an obtuse angle. Each inclination angle can be the same asor different from the other according to the first embodiment. A centerof hinge portion 37 is indicated by an axis C. A maximum height of hingeportion 37 is limited to approximately 25 mm. If the height thereofexceeds this, hinge portion 37 will have an excessive circumferentiallength and intrude into the storage space of air bag 9. The height isappropriately determined according to the particular material used forbacking member 22. Also, if the previously discussed inclination angleis too large, the inclination is a large obtuse angle and a distancebetween door-side portion 37 a and attachment-side portion 37 e of hingeportion 37 is too large, and it is also difficult to achieve acircumferential length for hinge portion 37. Therefore, the inclinationangle is preferably 150° at most.

Inflation Experiment I

Three instrument panels, i.e., cover bodies, with integrated air bagapparatuses were prepared according to the first embodiment of thepresent invention as shown in FIGS. 1 through 4 to serve as EXAMPLE I,EXAMPLE II, and EXAMPLE III. Each of the instrument panels was made frompolypropylene and each of the backing members from thermoplasticpolyolefin elastomer, having the physical properties shown in the tablebelow. Instrument panels with integrated air bag apparatuses wereprepared as examples of the related art for COMPARATIVE EXAMPLES Ithrough VIII. The inflation experiment was performed at a roomtemperature of 23° C. Results from observation of the experiment arealso presented in the table. Instrument panel (PP) Backing member (TPO)flexual flexual elastic tensile elastic tensile modulus strength Izodmodulus strength Izod MPa MPa kJ/m² elongation % MPa MPa kJ/m²elongation % Results of experiment EXAMPLE I 2,150 29.5 6.4 31 250 13570 NB Smooth inflation with inflation shape as designed. EXAMPLE II2,760 30.7 5.4 25 ″ ″ ″ ″ Same as above. EXAMPLE III 2,970 25.0 4.0 350″ ″ ″ ″ Same as above. COMP. EX. I 3,780 32.0 4.7 18 ″ ″ ″ ″ Tearsoutside tear seam, bag does not form planned inflation shape. Break-awayfragments. COMP. EX. II 1,270 19.6 3.2 10 ″ ″ ″ ″ Deforms under load,appearance-affecting pocket wave formed. COMP. EX. III 3,220 42.0 4.3 14″ ″ ″ ″ Inflation timing late. COMP. EX. IV 2,350 15.6 3.2 50 ″ ″ ″ ″Tears outside tear seam, bag does not form planned inflation shape.Break-away fragments. Inflation timing early. COMP. EX. V 2,220 15.814.7 360 ″ ″ ″ ″ Tears outside tear seam, bag does not form plannedinflation shape. Inflation timing early. COMP. EX. VI 2,460 26.8 17.4 70″ ″ ″ ″ Inflation timing late. COMP. EX. 3,420 36.0 2.8 6 ″ ″ ″ ″ Tearsoutside tear seam, bag does not form VII planned inflation shape.Break-away fragments. COMP. EX. 2,570 24.0 5.1 500 ″ ″ ″ ″ Inflationtiming late. VIIIInflation Experiment II

An instrument panel having an integrated air bag apparatus isconstructed to serve as COMPARATIVE EXAMPLE IX representative of therelated art, a hinge size thereof being of comparable largeness toEXAMPLE I, however, other than a shape in cross-section thereof being abent shape with no flat portion, a hinge thereof is the same that ofEXAMPLE I, as shown in FIG. 26A. Inflation of COMPARATIVE EXAMPLE IX wasobserved during an inflation experiment performed at a low temperatureof minus 30° C.

Results of the inflation experiment show that although the air bag ofCOMPARATIVE EXAMPLE IX inflated into a predetermined shape, stressevidenced by white blush marks at many locations occurred in theattachment-side portion of the hinge, and a crack designated by X formedin proximity to the tear seam. Partial breaking occurred in theinstrument panel where the crack had formed, shown in FIG. 26B.

In contrast, with EXAMPLE IV which used the same arrangement of EXAMPLEI, the door portion in the surface of instrument panel 1 swung withfavorable characteristics despite a low temperature of minus 30° C., andthere was no interference in the inflation of the air bag. Hinge portion37 was free from white blush marks produced by stress, damage, or otheradverse effects. Also, there was no cracking or fragmentation ininstrument panel 1.

A second embodiment according to the present invention will now beexplained. Reference numbering will be maintained for elements in commonwith the first embodiment, and explanation of common elements has beenabbreviated.

Referring to FIGS. 10 through 17, tear seam 24 comprises a first teargroove 24 a. Separation portion 20 is formed in an H-shape in a portionof backing member 22 which directly covers or corresponds to first teargroove 24 a. That is, separation portion 20 is formed in a portion ofbacking member 22 other than a portion corresponding to a front edgeportion and a back edge portion of first tear groove 24 a. Separationportion 20 is formed as a slit-shape of small width. A portion ofbacking member 22 which directly covers the front edge portion and backedge portion of first tear groove 24 a is hinge portion 37 which is abent shape and is disposed astride first tear groove 24 a. As shown inFIG. 11A, hinge portion 37 and first tear groove 24 a are relativelyaligned to form an off-center distance L1 between a hinge center 37 f ofhinge portion 37 and a groove center of first tear groove 24 a,off-center distance L1 being formed from 5 to 15 mm in the front andback direction of the surface of instrument panel 1. Hinge portion 37and first tear groove 24 a thus have a relative off-center alignment inthe surface direction.

Backing member 22 is larger in size than door portion 26, and aplurality of joining points 14 are formed both within the loop of tearseam 24 and beyond the loop of tear seam 24, as shown in FIGS. 10 to11B. Therefore, a portion of joining points 14 exist on door portion 26,and a portion of joining points 14 exist on a portion of backing portion22 not including door portion 26. Joining points 14 are formed byultrasonic welding, and work into or sink into instrument panel 1 frombacking member 22, such that the boundary surface between instrumentpanel 1 and backing member 22 takes on a waved shape. Joining strengthbetween the synthetic resin bodies is thereby increased.

According to the second embodiment of the present invention, hingeportion 37, 37 is formed in a U-shape in cross-section, and is formedintermittently in a plurality of portions in a left and right directionalong and under first tear groove 24 a, a pair of facing edge portionsexisting between each portion of hinge portion 37, 37 comprised of areinforcement edge portion and a surrounding edge portion. As shown inFIG. 11B, an extended supporting portion 23, 23 extends from one of thepair of facing edge portions existing between each portion of hingeportion 37, 37 toward attachment portion 17, 18 of backing member 22,and a free end portion 23 a of extended supporting portion 23, 23 comesin proximity to attachment portion 17, 18. In a first modification ofthe second embodiment, extended supporting portion 23, 23 is formed as apair of opposing members, each member of which extending from either ofthe two facing edge portions existing between each portion of hingeportion 37, 37, a free end portion 23 a of each member being in mutualproximity as well as mutually facing.

Upon collision of a vehicle, air bag 9 expands inside case 8, and bothdoor portion 26 as well as a portion of backing member 22 behind doorportion 26 are pushed upward by the force of expansion. Duringinflation, since a second tear groove 24 b which bridges both left andright sides of first tear groove 24 a is not covered by backing member22, the expansion force of air bag 9 is directly applied thereto andsecond tear groove 24 b easily tears. Also, by the groove center of boththe front edge portion and the back edge portion of first tear groove 24a being aligned off-center in the front and back direction with respectto hinge center 37 f of hinge portion 37, although first tear groove 24a is covered by extended supporting portion 23, 23 of backing member 22,extended supporting portion 23, 23 flexibly deforms with the expansionforce of air bag 9 since backing member 22 is made of soft syntheticresin, and the expansion force acts on corresponding portions of firsttear groove 24 a. Accordingly, even with normal-output inflator 4, firsttear groove 24 a and second tear groove 24 b tear properly, and doorportion is torn free from instrument panel 1, that is, from coveringportion 11.

Moreover, according to the second embodiment, attachment portion 17, 18is in proximity to first tear groove 24 a, and therefore air bag 9 isrestricted to upward movement toward first tear groove 24 a byattachment portion 17, 18. Thus, the expansion force of air bag 9 isconcentrated at first tear groove 24 a. As a result, further conditionsare provided which facilitate tearing of door portion 26.

Since each portion of hinge portion 37, 37 is U-shaped in cross section,each portion easily bends when door portion 26 opens. Also, extendedsupporting portion 23, 23 is disposed between each portion of hingeportion 37, 37 formed intermittently along first tear groove 24 a.Extended supporting portion 23, 23 extends from one of the facing edgeportions existing between each hinge portion 37, 37, and when doorportion 26 opens, free end portion 23 a of extended supporting portion23, 23 hits or contacts the other facing edge portion, and door portion26 bends without falling inward. Also, according to the previouslydescribed first modification of the second embodiment where extendedsupporting portion 23, 23 extends from each of the facing edge portionsbetween each hinge portion 37, 37, and each free end portion 23 a ofextending supporting portion 23, 23 are in mutual proximity, each freeend portion 23 a mutually hits or contacts when door portion 26 opens,and bending occurs from there without door portion 26 falling inward.

Door portion 26, which has been torn free from instrument panel 1,swings open in fore and aft directions centered about hinge portion 37of backing member 22, and from the opening formed by severed doorportion 26, air bag 9 expands into the vehicle interior to protect apassenger. Smooth expansion during inflation is promoted when air bag 9contacts the curved surface of hinge portion 37, 37.

A second modification of the second embodiment will be explained withreference to FIG. 12. An extended supporting portion 23 b of backingmember 22 is formed the same as extended supporting portion 23 of thesecond embodiment, except that extended supporting portion 23 b isjoined to attachment portion 17, 18 (only one facing portion thereof isshown) by a thinned portion 27. Thinned portion 27 of extendedsupporting portion 23 b covers a corresponding portion of first teargroove 24 a from directly beneath. However, since thinned portion 27also flexibly deforms, the corresponding portion of first tear groove 24a properly tears. Otherwise, this modification of the second embodimentis the same as the second embodiment.

A third modification of the second embodiment will be explainedreferring to FIG. 13. An extended supporting portion 23 c of backingmember 22 is joined to attachment portion 17, 18 (only one facingportion thereof is shown) by thinned portion 27. Thinned portion 27covers a corresponding portion of first tear groove 24 a from directlybeneath, however, the corresponding portion of first tear groove 24 aproperly tears since thinned portion 27 flexibly deforms. In this thirdmodification, a middle thinned portion 20 a is formed in backing member22 and covers second tear groove 24 b from beneath. Since middle thinnedportion 20 a flexibly deforms, the corresponding portion of second teargroove 24 b tears properly. Otherwise, this modification of the secondembodiment is the same as the second embodiment.

Referring to FIG. 14, a fourth modification of the second embodimentwill be explained. Backing member 22 is the same as that of the secondembodiment. A cover layer 28, which is thin and made from TPO resingiven a leather-like texture finish, covers instrument panel 1 includingdoor portion 26. Cover layer 28 is also therefore above first teargroove 24 a. Otherwise, this modification of the second embodiment isthe same as the second embodiment.

Referring to FIGS. 15, 16, and 17, cover layer 28 covers the surface ofinstrument panel 1 including the surface of covering portion 11. Coverlayer 28 is a soft resin sheet having a thickness approximately from 0.3to 1.5 mm. Before joining cover layer 28 with instrument panel 1, aplurality of holes 15 are formed along a portion thereof as aperforation portion to match with first tear groove 24 a to be formed inthe back surface of instrument panel 1 during after-processing. Holes 15are formed as open holes which are thus open at both an outer and aninner surface of cover layer 28.

A diameter of each hole of holes 15 is from 0.05 to 2.0 mm, preferablyfrom 0.2 to 0.3 mm, and a pitch between each hole is from 0.1 to 5.0 mm,preferably from 0.5 to 1.0 mm. Holes 15 are formed with a hole-formingtool having a plurality of projections which match with the diameter andpitch of holes 15 such as a machining blade or needle, or laser.

Next, the method of making instrument panel 1 and cover layer 28 as wellas operation thereof during use will be explained.

A soft resin sheet is first cut with a predetermined size to serve ascover layer 28, and holes 15 are formed therein at a location whichmatches with tear seam 24 which is formed in the back surface ofinstrument panel 1. Holes 15 are formed along tear seam 24 so as to forman H-shape in cover layer 28 as shown in FIG. 15. Holes 15 are formedwithin the diameter and pitch ranges specified above.

After cover layer 28 has been thus formed, cover layer 28 is inserted ina predetermined position in a mold for injection molding of aninstrument panel, and instrument panel 1 is formed by injection molding.

During injection molding, resin injected into the cavity of the mold isformed in a predetermined shape while flowing inside the cavity alongthe back side of cover layer 28. A part of the resin also flows intoholes 15 previously formed in cover layer 28.

However, the flow of resin into holes 15 is restricted to as far asopening portion 15 a which is an end of holes 15 at the outside surfaceof cover layer 28. Restriction of flow is caused by a flow regulatingeffect which occurs naturally from the aforementioned predetermineddimensions of holes 15, and also by the pressure of gas built up inholes 15 and packed by the opposing mold surface, as well as by thepressure of gas emitted by resin melt during the injection process. Asshown in FIG. 16, flow of resin is stopped just before the outer edge ofopening portion 11 a.

Once the injection molding of instrument panel 1 has been completed,instrument panel 1 is left to cure. Joined instrument panel 1 includingcovering portion 11 and cover layer 28 are then removed from the mold asan integral structure with the surface of instrument panel 1 beingcovered by cover layer 28. Also, a portion of holes 15 not all the wayto opening portion 15 a thereof is sealed by a portion of the rigidresin which forms instrument panel 1, a large portion of holes 15 thusbeing in a solid condition due to the rigid resin, and problemsincluding swelling due to pressure of resin during the formation processdo not occur.

The rigid resin is rated with a melt flow rate of from 10 to 30 (JISK-7210), preferably in a range centered around 15. According to thisembodiment, grade HIP145 MFR14.2 (Grand Polymer Co., Ltd.) was used,which is a polypropylene (polypropylene composite, PPC) containing talc.

Once air bag 9 starts to expand, door portion 26 is pushed open by theforce of expansion centered on hinge portion 37. Therefore, tear seam 24formed in instrument panel 1 which covers backing member 22 tearssubstantially in an H-shape, cover layer 28 thereby also being tornalong tear seam 24 due to holes 11 formed therein. Thus, even in aninstance where a material which is relatively difficult to tear is usedfor cover layer 28, cover layer 28 tears properly in a predeterminedshape.

Referring to FIG. 17, a fifth modification of the second embodiment isshown. In this modification, each hole of holes 15 is formed in coverlayer 28 as blind holes 15 b, and thus are open only at an end thereofin the inner surface of cover layer 28. Resin flowing into blind holes15 b seals in air pre-existing in blind holes 15 b as well as gas whichis emitted from the very melting resin, and therefore, since pressingpressure of resin is not directly applied to a bottom of blind holes 15b, swelling does not occur in the surface of cover layer 28 at portionsthereof directly over blind holes 15 b during cooling and hardening ofthe resin.

According to this fifth modification, sink marks resulting fromformation of first tear groove 24 a and second tear groove 24 b iscovered and concealed. Otherwise, this modification of the secondembodiment is the same as the second embodiment.

By providing extended supporting portion 23 between intermittentlyformed hinge portion 37, support is provided where there is otherwisespace existing between portions of hinge portion 37, it is not necessaryfor covering portion 11 to possess a high impact resistance which isotherwise normally required in an instrument panel, and thus a costreduction is realizable. Also, tearing at portions other than tear seam24 is prevented.

A third embodiment according to the present invention will be explainedwith reference to FIGS. 18 to 22. Reference numerals are maintained forelements in common with the previous embodiments. Explanation of someelements in common with the previous embodiments will be found.

Backing member 22 is formed as a single and integral body whichcomprises inner surrounding portion 35 which is a square plate framemember fixed to a back side of outer surrounding portion 25 ofinstrument panel 1, attachment portion 17, 18 which comprises a frontfacing portion and a back facing portion which form a square tube shapeprojecting downward from an edge portion of an inner circumference ofinner surrounding portion 35, a door reinforcement portion 33, 33 whichcomprises a pair of square plate shape members, each being fixed to aback side of one of two members of door portion 26, 26 and thus locatedwithin the inner circumference of inner surrounding portion 35, hingeportion 37, 37 which comprises a plurality of portions which joins doorreinforcement portion 33, 33 to the front and back portions ofattachment portion 17, 18, extended supporting portion 23 which isformed between each portion of hinge portion 37, 37 and extends fromdoor reinforcement portion 33, 33 toward attachment portion 17, 18, anda joining portion 70 which serves as a connection between extendedsupporting portion 23 and attachment portion 17, 18. Inner surroundingportion 35 and attachment portion 17, 18 constitute a surrounding base34. Also, separation portion 20 is formed as a concave groove having asmall width between each member of door reinforcement portion 33, 33, aswell as along both short edge portions on both sides of doorreinforcement portion 33, 33. That is, separation portion 20 is formedin a substantial H-shape along a position facing the short edge portionsof first tear groove 24 a as well as facing second tear groove 24 b in amiddle of door portion 26, 26.

Each portion of hinge portion 37, 37 is deformable, and is flexibleaccording to the third embodiment. According to the third embodiment,hinge portion 37, 37 comprises a plurality of portions, for example, 5portions, which are disposed at predetermined intervals along a positionfacing a portion of tear seam 24, according to the third embodiment,along a position facing a front groove portion and a rear groove portionof first tear groove 24 a located respectively at a front and back ofdoor portion 26, 26. Hinge portion 37, 37 is not limited to comprising 5portions nor to the manner in which hinge portion 37, 37 is deformable.The portions of hinge portion 37, 37 are disposed astride first teargroove 24 a, and flexibly connect each member of door reinforcementportion 33, 33 with attachment portion 17, 18, that is, each member ofdoor reinforcement portion 33, 33 with surrounding base 34. As shown inFIG. 18, one end of hinge portion 37, 37 joins with door reinforcementportion 33, 33, and another end thereof joins with attachment portion17, 18, and a curved portion 41 is provided in a downward-projectingmanner, such that hinge portion 37, 37 projects or bulges downward,curved portion 41 being arcuate in cross-section, and further, areU-shaped or V-shaped in cross-section.

Further, extended supporting portion 23 is disposed to be in proximityto hinge portion 37, 37, and according to the third embodiment, isdisposed between adjacent portions of hinge portion 37, 37, as well asat the front groove portion and the rear groove portion of first teargroove 24 a, and extends from door reinforcement portion 33, 33 towardattachment portion 17, 18 as a square flat-shaped tongue. Each extendedsupporting portion 23 is fixed along with door reinforcement portion 33,33 through a process such as vibration welding to a back side of doorportion 26 of instrument panel 1, and adds to the joining strengthbetween backing member 22 and instrument panel 1 by adding additionaljoining surface area.

Joining portion 70, which serves as a connecting member between extendedsupporting portion 23 and attachment portion 17, 18, is projectinglydisposed on a lower edge of an edge portion of extended supportingportion 23, that is, along a position distanced from instrument panel 1,in a square flat shape. Joining portion 70 is significantly thinner thanextended supporting portion 23, being designed to tear during inflationof air bag 9.

Further, according to the third embodiment, extended supporting portion23 and curved portion 41 of hinge portion 37, 37 share a thickness D1 of3.0 mm, which is the same as a shared thickness of inner surroundingportion 35 of backing member 22 and door reinforcement portion 33, 33.Also, joining portion 70 is formed with a set thickness D2 of 1.5 mm.Also, a height L2 of a space portion 44 is set at 2.5 mm, space portion44 existing between an inner surface of instrument panel 1, i.e., aninner surface of covering portion 11, and a location on attachmentportion 17, 18 distanced from instrument panel 1 where hinge portion 37,37 is joined.

Further, a depth H1 from a top-side surface of door reinforcementportion 33 of backing member 22 to an bottom-side surface of a lowermostend of hinge portion 37, 37 is 12.5 mm, a depth H2 from the top-sidesurface of door reinforcement portion 33 to a top-side surface of alowermost end of hinge portion 37 is 10.0 mm, an outer width W1 of aconcave portion formed by curved portion 41 at an top-side surface ofbacking member 22, that is, a combined length of extended supportingportion 23 and joining portion 70, is 16.5 mm, and a width W2 which is alength of joining portion 70 is 4.8 mm. Further, dimensions of eachelement, such as height L2 of space portion 44, are determined uponconsideration of various factors including characteristics of resinused, size of air bag 9, i.e., volume and shape, gas injectioncharacteristics and specifications of inflator 4, as well as uponconsideration of results of inflation testing of air bag apparatus 3.

Next, operation of instrument panel 1 with integrated air bag apparatus3 will be explained.

Gas is injected into air bag 9 which then inflates inside case 8.Inflation force of air bag 9 works through door reinforcement portion 33of backing member 22 to force door portion 26 of instrument panel 1 tobulge. During inflation, as shown by the solid line in FIG. 19, inaddition to hinge portion 37, 37, joining portion 70 is also joined todoor portion 26, 26 at a portion thereof along first tear groove 24 aand functions to control the range of movement of door portion 26, 26,such that each member of door portion 26, 26 swings open in a directionindicated by Fb and Fc respectively. Inflation force of air bag 9 forcesseparation portion 20 and tear seam 24 from second tear groove 24 b totear, and further, tear seam 24 tears along an entire length thereof,and door portion 26, 26 is torn free from remaining portions ofinstrument panel 1, to form a freed door portion which includes doorportion 26, 26. Tearing of joining portion 70 occurs at a point in timefrom before to after formation of the freed door portion, and eachmember of the freed door portion swings with hinge portion 37 serving asa support, and an opening for air bag 9 to inflate through is formed.

Thus, according to the third embodiment, tearable joining portion 70 isdisposed in proximity to hinge portion 37 of backing member 22, and doorportion 26 and surrounding base 34 are connected with joining portion70. Therefore, behavior of door portion 26 is regulated during theinitial expansion stage by joining portion 70, and door portion 26 andthe freed door portion are formed with desirable characteristics.

That is, according to the third embodiment, since joining portion 70 andhinge portion 37 are disposed along first tear groove 24 a, upwardbulging and tearing are controlled where hinge portion 37 is disposed byjoining portion 70, and tearing of tear seam 24 at locations other thanwhere hinge portion 37 is disposed occurs first, and swinging movementof door portion 26 and the entire freed door portion are promoted, and,door portion 26 and the entire freed door portion swing open with stablecharacteristics with disregard for changes in resin characteristics dueto temperature changes.

If joining portion 70 were not provided, then in a high temperaturerange such as at temperatures in excess of 100° C., the entirety of doorportion 26, 26 bulges upward in the direction indicated by arrow Aduring expansion of air bag 9, and second tear groove 24 b as well asthe remainder of tear seam 24 tear all at once, after which door portion26, 26 may behave in a crank-like manner where the members of doorportion 26, 26 move in a lateral direction in parallel as indicated bythe broken-line arrows Gb and Gc in FIG. 19. The freed door portion hasan edge portion formed by tearing at portions including the front grooveportion and the rear groove portion of first tear groove 24 a, the edgeportion being where the freed door portion is joined by hinge portion70, and in such an instance where joining portion 70 is not provided,the edge of the freed door portion moves into a position where movementthereof is limited while rubbing with an outer surface 21 a ofinstrument panel 1, and door portion 26, 26 is pushed upward in thedirection of arrow A while outer surface 21 a interferes with movementthereof and prevents any further movement sideways thereof, and a largeamount of force may come to act at locations including a joining face 22a of instrument panel 1 and backing member 22 and hinge portion 37. Incontrast, according to the third embodiment, the edge formed by tearingat portions including the front groove portion and rear groove portionof first tear groove 24 a suppresses interference with outer surface 21a of instrument panel 1, and desired characteristics are stablymaintained.

Also, joining portion 70 is disposed on backing member 22, and tearingcharacteristics of the front groove portion and the rear groove portionof first tear groove 24 a facing hinge portion 37, 37 are formed equallywith other portions of tear seam 24. Therefore, during inflation of airbag 9, the front groove portion and the rear groove portion of firsttear groove 24 a tears in the same rapid manner. Thus, during theinitial inflation stage, the edge of the freed door portion formed bytearing of the front groove portion and the rear groove portion of firsttear groove 24 a is smoothly pulled into space portion 44, andinterference between the edge of the freed door portion and outersurface 21 a of instrument panel 1 is suppressed. Further, since tearseam 24 which includes first tear groove 24 a does not need to bedesigned with a special shape, a shape of the edge of the freed doorportion is easily made to be smooth.

Therefore, air bag 9 is maintained with desirable characteristics toenable smooth inflation thereof, whether in a low temperature range or ahigh temperature range. Air bag 9 also has both favorable movementduring inflation and a favorable outer appearance. A favorable structureis thus provided for air bag apparatus 3 formed integrally withinstrument panel 1.

Also, according to the third embodiment, since hinge portion 37comprising several portions is disposed astride tear seam 24 along aportion where door reinforcement portion 33 and surrounding base 34mutually face, and joining portion 70 is disposed between adjacentportions of hinge portion 37, 37, along a predetermined portion, thatis, along the front groove portion and the rear groove portion of firsttear groove 24 a, support is provided by hinge portion 37 while upwardbulging is suppressed, and desired swinging movement is therebyrealized.

Further, according to the third embodiment, since extended supportingportion 23 extends from door reinforcement portion 33, 33 betweenportions of hinge portion 37, by joining extended supporting portion 23along with door reinforcement portion 33 to door portion 26, 26, joiningsurface area is increased, and a single, reinforced body is achieved asfar as a position in proximity to surrounding base 34, therebyincreasing rigidity. Further, it is only necessary for joining portion70 to connect across a very small space, and thus joining portion 70 canbe designed with a small length, and therefore upward bulging of doorportion 26, 26 is effectively suppressed, and door portion 26, 26 openswith a favorable motion.

Also, according to the third embodiment, a height of an upper surface ofhinge portion 37, 37 at a base portion thereof joined to attachmentportion 17, 18 is set at a position lower than a height of an uppersurface of both inner surrounding portion 35 and door reinforcementportion 33, 33, space portion 44 being thereby formed between instrumentpanel 1 and backing member 22, therefore, the freed door portion swingswith a low-positioned point of support, that is, the edge of the freeddoor portion formed by tearing of tear seam 24 swings so as to be pulleddownward into space portion 44, and further, the edge of the freed doorportion is pulled into a space formed by curved portion 41 of hingeportion 37, 37, and is thereby enabled to swing smoothly.

Further, it is not necessary for joining portion 70 to be disposed atboth the front groove portion and the rear groove portion of first teargroove 24 a. As a first modification of the third embodiment, joiningportion 70 is formed only at the rear groove portion, that is, a portionof first tear groove 24 a nearest a passenger. Otherwise, thismodification of the third embodiment is the same as the thirdembodiment.

Also, a shape of joining portion 70 does not necessarily need to beformed in a flat plate shape, and can be any shape which allows joiningportion 70 to act as a regulating member which regulates movement to apredetermined position, and constitutes a point of pivot for swingingduring the initial inflation stage.

Further, joining portion 70 is formed to be tearable, and tears duringinflation of air bag 9 as previously explained, however, depending onconditions, for example, under high temperatures, joining portion 70 maybe formed as a structure which allows smooth formation of door portion26 and the freed door portion without tearing. Also, as a secondmodification of the third embodiment, joining portion 70 is designedsuch that under certain temperature conditions, only a predeterminednumber of the portions which constitute joining portion 70 tear and theremainder thereof are left untorn, as opposed to allowing all of joiningportion 70 to tear. Otherwise, this modification is the same as thethird embodiment.

Also, although separation portion 20 disposed between each member ofdoor reinforcement portion 33, 33 is formed in a concave groove shapeaccording the third embodiment, as a third modification of the thirdembodiment, separation portion 20 is formed as a perforation such thatthe members of door reinforcement portion 33, 33 are intermittentlyjoined. In a further fourth modification, separation portion 20 isformed as a fully divided and continuous slit. Otherwise, the third andfourth modifications of the third embodiment are the same as the thirdembodiment.

A fourth embodiment according to the present invention will now beexplained with reference to FIGS. 23 through 25. Reference numerals aremaintained for elements in common with the previous embodiments.Explanation of common elements is abbreviated.

As shown in FIG. 23, hinge portion 37 comprises curved portion 41 whichis joined at one end thereof to door reinforcement portion 33, and alowered joint portion 42 which is joined to another end of curvedportion 41 and attachment portion 17, 18 and faces tear seam 24 so as tosuperimpose tear seam 24. Curved portion 41 is arcuate in cross section,and further, is formed substantially in a U-shape in cross section, andhas a bent surface portion facing downward toward a bottom of air bag 9,that is, the bent surface bulges downward toward a bottom of air bagapparatus 3. Lowered joint portion 42 is formed in a horizontal plateshape. Further, a height of an upper surface of lowered joint portion42, which constitutes a base of hinge portion 37 of backing member 22and is joined to attachment portion 17, 18, is set at a lower positionthan a shared height of an upper surface of inner surrounding portion 35and door reinforcement portion 33, that is, lower than a height of alower surface of instrument panel 1, this difference in heights beingindicated as height L3 in FIG. 23. Thus, an open space portion 74 isformed between lowered joint portion 42 and first tear groove 24 a ofinstrument panel 1, and is enclosed by hinge portion 37, attachmentportion 17, 18, and outer surrounding portion 25.

Further, according to the fourth embodiment, a height L3 is set at 2.5mm. Also, curved portion 41 and lowered joint portion 42 of hingeportion 37 are formed with a set thickness D3 of 3.0 mm which is thesame as a shared thickness of inner surrounding portion 35 of backingmember 22 and door reinforcement portion 33. Also, a depth H3 from a topsurface of door reinforcement portion 33 of backing member 22 to abottom surface of a lowermost edge of hinge portion 37 is 12.5 mm, and adepth H4 from a top surface of door reinforcement portion 33 to a topsurface of a lowermost edge of hinge portion 37 is 10.0 mm, a concaveportion width W3 of a concave portion of curved portion 41 of hingeportion 37 at the top surface of backing member 22 is 16.5 mm, and aspace portion width W4 across a top surface of lowered joint portion 42between a location where lowered joint portion 42 joins attachmentportion 17, 18 and a location where lowered joint portion 42 joinscurved portion 41 is set at 4.8 mm, which is substantially the same aswidth of a bottom edge of tear seam 24.

Therefore, dividing hinge portion 37 about a central low point B, adoor-reinforcement-portion side length, i.e., a length along curvedportion 41 from door reinforcement portion 33 to central low point B, islarger than an inner-surrounding-portion side length, i.e., a lengthalong lowered joining portion 42 and curved portion 41 from attachmentportion 17, 18 to central low point B.

Further, dimensions of each element, such as height L3 of open spaceportion 74, are set with consideration of various factors includingcharacteristics of resin used, size of air bag 9, i.e., volume, shape,injection characteristics and specifications of inflator 4, as well aswith consideration of inflation test results of air bag apparatus 3.

Once air bag 9 inflates upon injection of gas, as previously explained,door portion 26 is torn free from other portions of instrument panel 1,i.e, from covering portion 11, and as is shown in FIG. 24A, door portion26 commences swinging, that is, formation, as a freed door portion 76.

Next, freed door portion 76 swings with a particular point within openspace portion 74 as an axis, and an opening for air bag 9 to expandthrough is formed.

According to the fourth embodiment, lowered joint portion 42, which is abase of hinge portion 37, is joined to attachment portion 17, 18, andthe height of the top surface of lowered joint portion 42 is set at alower position than the height of the top surface of inner surroundingportion 35 and door reinforcement portion 33, and open space portion 74is formed between instrument panel 1 and backing member 22. Thus, freeddoor portion 76 swings with a lower point of support, than if loweredjoint portion 42 were not set at a lowered position and instead were setat a position equal in height to inner surrounding portion 35 and doorreinforcement portion 33. Also, having an edge portion 47 formed on doorportion 76 by tearing of tear seam 24, as shown in FIG. 24B, freed doorportion 76 swings so as to be pulled into open space portion 74 locatedtherebelow, and further, edge portion 47 of freed door portion 76 ispulled into a space formed by curved portion 41 of hinge portion 37, andthereby swings smoothly.

Thus, according to the fourth embodiment, lowered joint portion 42,which serves as an inner-surrounding-portion side base of hinge portion37, is joined to attachment portion 17, 18, and a joining location oflowered portion 42 is at a distance downward from a boundary portionexisting between instrument panel 1 and inner surrounding portion 35,and open space portion 74 is formed at the boundary portion on a side ofattachment portion 17, 18 which acts as a hinge base of innersurrounding portion 35 for hinge portion 37, therefore, during inflationof air bag 9, freed door portion 76 formed by tearing of tear seam 24swings with a low point of pivot, and since edge portion 47 of freeddoor portion 76 enters open space portion 74, freed door portion 76maintains desirable characteristics and is formed smoothly.

In contrast, an example of the related art is given. With reference toFIG. 27A, a base of a hinge portion 370 is joined to an innersurrounding portion 250 a at the same height as a door reinforcementportion 330. Under extreme high temperature conditions, referring toFIG. 27B, there are occurrences of an edge portion 470 of a freed doorportion 460 forming and swinging such that edge portion 470 rides on anouter surface of an instrument panel 220, and it is difficult for freeddoor portion 460 to be stabilized or maintained with desirablecharacteristics and form smoothly. As regards this matter, according tothe fourth embodiment of the present invention, edge portion 47 of freeddoor portion 76 maintains desirable characteristics without riding onthe outer surface of instrument panel 1.

Also, in a modification of the fourth embodiment, a portion ofattachment portion 17, 18 which faces open space portion 74 is used as aguide portion for guiding edge portion 47 of freed door portion 76, suchthat characteristics are easily maintained for forming and swingingmovement of freed door portion 76.

As shown in FIG. 25, a guide portion 48 is disposed at a portion ofattachment portion 17, 18 which faces open space portion 74, guideportion 48 being an inclined surface which inclines toward curvedportion 41 of hinge portion 37. According to this modification, duringforming and swinging of freed door portion 76, edge portion 47 of freeddoor portion 76 slidingly contacts guide portion 48, and is guided intoopen space portion 74, and stable characteristics are easily achievedfor forming and swinging movement of freed door portion 76. Further,guide portion 48 can be formed with either a flat surface or with acurved surface. Otherwise, this modification of the fourth embodiment isthe same as the fourth embodiment.

Although in the fourth embodiment door portion 26 was formed with twoportions so as to open in a double-door manner, door portion 26 can alsobe formed with a single portion.

This application is based on prior Japanese Patent Applications No.2002-277418, No. 2002-287965, No. 2002-346434, No. 2003-115646, No.2003-181801, and No. 2003-181802. The entire contents of Japanese PatentApplications No. 2002-277418 with a filing date of Sep. 24, 2002, No.2002-287965 with a filing date of Sep. 30, 2002, No. 2002-346434 with afiling date of Nov. 28, 2002, No. 2003-115646 with a filing date of Apr.21, 2003, No. 2003-181801 with a filing date of Jun. 25, 2003, and No.2003-181802 with a filing date of Jun. 25, 2003 are hereby incorporatedby reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

1. A cover body covering an air bag apparatus, the cover body beingintegral with an interior panel of a vehicle, the cover body comprising:a covering portion which is formed integrally with an interior panelbody, the covering portion having a door portion defined by a tear seamin a closed-loop shape in a back surface of the interior panel body; anda backing portion which is joined to a back of the covering portionincluding the door portion, the backing portion being made ofthermoplastic olefin which is softer and has a greater elongation thanthe polyolefin resin; wherein the backing portion comprises areinforcing portion joined to a back surface of the door portion, asurrounding base which is joined to the back surface of the coveringportion surrounding the door portion and having an attachment portion,and a hinge portion having an end joined to the reinforcing portion andanother end joined to an edge portion of the surrounding base at alocation away from the back surface of the covering portion so that theedge portion of the surrounding base forms a space between the backsurface of the covering portion and the hinge portion.
 2. The cover bodyas claimed in claim 1, wherein the hinge portion comprises a U-shapedportion having two ends and a curved surface portion definedtherebetween, wherein one end is lined to the reinforcing portion andanother end is linked to the surrounding base and a curved surfaceprotrudes toward an air bag stored within the air bag apparatus, and alower joint portion is arranged in the backing portion so that the lowerjoint portion substantially superposes the tear seam of the coveringportion.
 3. The cover body as claimed in claim 2, wherein thesurrounding base comprises a guide portion facing the space portion toguide an edge portion of the door portion which is formed by tearing ofthe tear seam.